A paradigm shift for a new class of proton exchange membranes with ferrocyanide proton-conducting groups providing enhanced oxidative stability

A new class of proton exchange membranes (PEMs) containing ferrocyanide groups as both proton-conducting/radical scavenger components are fabricated. Here, the ferrocyanide groups are bonded to a commercial fluoroelastomer polymer main chain, resulting in ferrocyanide-coordinated PEMs (CFC) for proton exchange membrane fuel cells (PEMFCs). The CFC PEMs show a larger hydrophilic morphological phase than Nafion 212 membrane, even in the CFC having lower ion exchange capacity, owing to stronger electrostatic forces among ferrocyanide groups than traditional sulfonic groups. Compared with Nafion 212, CFC membranes present inferior proton conductivity in water. However, they show much lower activation energy for proton transport in water, and considerably higher proton conductivity than Nafion 212 under low relative humidity (RH). This is related to the larger hydrophilic domains that may construct better-connected channels for proton transport, especially at low membrane hydration levels. As a result, CFC membranes exhibit better power output than Nafion 212 in PEMFC evaluations under low RH conditions. The chemical accelerated stress test (AST) demonstrates that the radical scavenging ability of ferrocyanide group is effective for greatly reducing electrochemical oxidation .